Control and diagnostics of multiple electrical generating machines using an external voltage regulator

ABSTRACT

An electrical system for an automotive vehicle has a plurality of electrical generating machines having field windings energized by pulse width modulated drive signals generated by an external electronic voltage regulator. The pulse width modulated drive signals have a duty cycle determined by the electronic voltage regulator. A controller selects one of electrical generating machines to evaluate for failure and evaluates that electrical generating machine for failure by causing the PWM drive signal for the field windings of that electrical generating machine to be disabled. The controller then determines that this electrical generating machine has failed if the duty cycle for the PWM drive signals has then not been increased by the electronic voltage regulator by a pre-determined amount. The electrical generating machines are either generators or alternators. In an aspect, the PWM drive signals for the plurality of electrical generating machines are out of phase with each other.

FIELD

The present invention relates to the control and diagnostics of multipleelectrical generating machines using an external voltage regulator.

BACKGROUND

In certain types of vehicles, such as medium and heavy duty trucks, itis advantageous to provide the electrical system with multipleelectrical generating machines, which are alternators or generatorsdepending on whether the electrical system uses alternators orgenerators. For convenience the discussion herein will be the context ofalternators, it being understood that it also applies to generators.

A voltage regulator is used to regulate the output voltage of thealternator. Typically, the voltage regulator varies the voltage of thefield of the alternator to regulate the output voltage of thealternator. In many applications, the alternator has an internal voltageregulator.

In certain applications having a single alternator, an externalelectronic voltage regulator has been used. In one such application, theexternal electronic voltage regulator is implemented in the electroniccontrol unit (ECU) that is also used as the engine control module of avehicle. In this application, the external voltage regulator outputs apulse width modulated drive signal to the field winding of thealternator and varies field voltage of the alternator to regulate theoutput voltage of the alternator by varying the duty cycle of the pulsewidth modulated signal. As used herein, an “electronic voltageregulator” is a device that generates a pulse width modulated drivesignal that is used to energize the field windings of an electricalgenerating machine. The device can be implemented in hardware or acombination of hardware and software. The device can be a stand-alonedevice or can be implemented as part of another device, such as theengine control module of a vehicle. The electronic voltage regulator cangenerate the pulse width modulated drive by directly generating it orgenerate it by controlling another device, such as a power switchingdevice by generating a pulse width modulated switching signal that isused to switch the power switching device.

FIG. 1 is a basic schematic showing the topology of a prior artelectrical system 100 in which an external electronic voltage regulatoris used to control the voltage of an alternator. Electrical system 100is illustratively an automotive vehicle electrical system and is a partof an automotive vehicle, shown representatively by dashed box 102 inFIG. 1. The external electronic voltage regulator is illustrativelyimplemented in an electronic control unit (“ECU”) 110, that is also theengine control module for vehicle 102. More specifically, electricalsystem 100 has an alternator 104, battery 106, power distribution center108 and ECU 110 that is the engine control module. ECU 110 includes anelectronic voltage regulator 112 that controls the field voltage offield windings 114 of alternator 104. A voltage output (B+) ofalternator 104 is coupled through a fusible link 116 to a positiveterminal 118 of battery 106. A negative terminal 120 of battery 106 iscoupled to ground.

Electronic voltage regulator includes error signal generator 122, PIcontroller 124, PWM signal generator 126 and power signal driver 128,which is illustratively a high side driver and may be referred to hereinas high side driver 128.

The control of alternator 104 is managed by the electronic voltageregulator 112 in ECU 110 based on voltage feedback sense line “B+ Sense”coupled to a “B+ sense” output of alternator 104, which is coupled tothe internal voltage output of alternator 104 through a B+ resistor.This sense voltage is compared by error signal generator 122 to a targetvoltage determined by the ECU 110 based on various parameters known tothe ECU 110 from other sensors in the electrical system 100 (not shownin FIG. 1), such as battery temperature, engine speed, engine load andothers. The comparison between the sense voltage and the target voltageproduces an error signal which is used by PI controller 124 ofelectronic voltage regulator 112 to calculate the duty cycle for a PWMdrive signal applied to field windings 114 of alternator 104 to controlthe field voltage and thus regulate the output of alternator 104. Thefield windings 114 of alternator 104 are coupled to an output 130 of ECU110 at which the PWM drive signal is generated. More specifically, PIcontroller 124 of electronic voltage regulator 112 determines the dutycycle at which to drive the field windings 114 of alternator 104 andoutputs to PWM signal generator 126 the value of this duty cycle, whichis the PWM value in FIG. 1. PWM signal generator 126 generates a PWMsignal having this duty cycle which is used to switch high side driver128, which turns on and off the field of alternator 104. High sidedriver 128 is coupled through contacts 132 of an automatic shutdownrelay (ASD) 134 of power distribution center 108 and a fuse 136 of powerdistribution center 108 to positive terminal 118 of battery 106. Highside driver 128 may illustratively be high power switching semiconductordevice, such as an SCR, Thyristor, IGBT, power MOSFET, or the like. Theobjective of this control system is to minimize the error signal, whichimplies that the sense voltage is being controlled to achieve the targetvoltage. The PI loop in PI controller 124 of electronic voltageregulator 112 is calibrated to optimize the overshoot, undershoot andsettling time performance specifications for system voltage response tovarious disturbances.

SUMMARY

In accordance with an aspect of the present disclosure, an electricalsystem for an automotive vehicle has a plurality of electricalgenerating machines. Each electrical generating machine includes fieldwindings energized by pulse width modulated drive signals generated byan external electronic voltage regulator. The pulse width modulateddrive signals have a duty cycle determined by the electronic voltageregulator. The electronic voltage regulator varies the duty cycle of thepulse width modulated drive signals to control output voltages of theelectrical generating machines. A controller selects one of electricalgenerating machines to evaluate for failure. The controller evaluatesthat electrical generating machine for failure by causing the PWM drivesignal for the field windings of that electrical generating machine tobe disabled. The controller then determines that this electricalgenerating machine has failed if the duty cycle for the PWM drivesignals has then not been increased by the electronic voltage regulatorby a pre-determined amount after the PWM drive signal for the fieldwindings of that electrical generating machine has been disabled. Theelectrical generating machines are either generators or alternators.

In an aspect, the controller evaluates in turn each of the electricalgenerating machines.

In an aspect, the PWM drive signals provided to each of the fieldwindings of each of the electrical generating machines are out of phasewith each other. In an aspect, the PWM drive signals are out of phasewith each other a number of degrees determined by 360/X where X is thenumber of electrical generating machines that the electrical system has.

In an aspect, the field windings of each electrical generating machineare coupled to respective power signal drivers that are switched at theduty cycle to generate the PWM drive signals.

In an aspect, the controller is an engine control module and includesthe electronic voltage regulator.

In an aspect, there is a separate electronic voltage regulatorassociated with each electrical generating machine that controls theduty cycle of the PWM drive signal provided to the field winding of thatelectrical generating machine. In an aspect, the engine control moduleincludes each external voltage regulator.

Further areas of applicability of the teachings of the presentdisclosure will become apparent from the detailed description, claimsand the drawings provided hereinafter, wherein like reference numeralsrefer to like features throughout the several views of the drawings. Itshould be understood that the detailed description, including disclosedembodiments and drawings referenced therein, are merely exemplary innature intended for purposes of illustration only and are not intendedto limit the scope of the present disclosure, its application or uses.Thus, variations that do not depart from the gist of the presentdisclosure are intended to be within the scope of the presentdisclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified schematic of a prior art vehicle electricalsystem having an alternator and an external electronic voltageregulator;

FIGS. 2A and 2B are a simplified schematic of a vehicle electricalsystem having multiple electrical generating machines having fieldwindings energized by pulse width modulated drive signals controlled byan external electronic voltage regulator in accordance with an aspect ofthe present disclosure;

FIGS. 3A and 3B are a flow chart of an evaluation routine for evaluatingfor failure the electrical generating machines of the vehicle electricalsystem of FIG. 2; and

FIG. 4 is a graph showing pulse width modulated drive signals for twoelectrical generating machines that are out of phase with each other inaccordance with an aspect of the present disclosure; and

FIG. 5 is a simplified block diagram of a vehicle electrical systemhaving multiple electrical generating machines each having fieldwindings energized by pulse width modulated drive signals controlled bya respective external electronic voltage regulator in accordance with anaspect of the present disclosure.

DETAILED DESCRIPTION

Referring to FIG. 2, an electrical system 200 having multiple electricalgenerating machines having fields controlled by external voltageregulators is shown. While the following will be described withreference to alternators, it should be understood that it also appliesto generators. Electrical system 200 is illustratively an automotivevehicle electrical system and included in an automotive vehicle, shownrepresentatively by dashed box 202 in FIG. 2.

Electrical system 200 is for use in vehicles where it is advantageous tohave multiple alternators. In the illustrative example shown in FIG. 2,electrical system 200 has two alternators, Alternator A (also identifiedwith reference numeral 204) and Alternator B (also identified withreference numeral 206). But it should be understood that electricalsystem 200 could have more than two alternators. In the illustrativeexample shown in FIG. 2, electrical system 200 also has two batteries,Battery A (also identified with reference numeral 208), and Battery B(also identified with reference numeral 210). But it should beunderstood that electrical system 200 could have other than twobatteries. For example, if electrical system 200 has more than twoalternators, it may have a corresponding number of batteries. It mayalso have a single battery.

Alternator A has an internal positive voltage output 212 coupled to apositive output voltage terminal 214 and a negative terminal 220 coupledto ground. Positive output voltage terminal 214 is coupled throughfusible link 216 to a positive terminal 218 of battery A. A negativeterminal 222 of battery A is also coupled to ground. Alternator A has avoltage sense output 224 coupled through a current limiting resistor 226to an internal positive voltage output 212 of alternator A.

Alternator B has an internal positive voltage output 228 coupled to apositive output voltage terminal 230 and a negative terminal 236 coupledto ground. Positive output voltage terminal 230 is coupled throughfusible link 232 to a positive terminal 234 of battery B. A negativeterminal 238 of battery B is also coupled to ground. Alternator B has avoltage sense output 240 coupled through a current limiting resistor 242to internal positive voltage output 228.

An electronic control unit (“ECU”) 244 has an electronic voltageregulator 246 implemented therein. ECU 244 is illustratively an enginecontrol module of vehicle 202. Electronic voltage regulator 246 includeserror signal generator 248, PI controller 250, PWM enable 252 (forAlternator A), PWM enable 254 (for Alternator B), PWM signal generator256 (for Alternator A), PWM signal generator 258 (for Alternator B),power signal driver 260 (for Alternator A), and power signal driver 262(for Alternator B). ECU 244 also includes voltage sense inputs 264, 266coupled to error signal generator 248, voltage target generator 268coupled to error signal generator 248, and battery voltage input 270coupled to error signal generator 248. Battery voltage input 270 iscoupled through fuse 136 of power distribution center 108 to positiveterminals 218, 234 of batteries A and B. Voltage sense input 264 iscoupled to voltage sense output 224 of alternator A and voltage senseinput 266 is coupled to voltage sense output 240 of alternator B.

Error signal generator 248 is illustratively implemented in softwareprogrammed in ECU 244 as is PI controller 250. PWM enables 252, 254 arealso illustratively implemented in software programmed in ECU 244. EachPWM signal generator 256, 258 are also illustratively implemented insoftware programmed in ECU 244 and each generates a PWM signal having aduty cycle corresponding to a data value provided by PI controller 250at data inputs 281, 282 of PWM signal generators 256, 258, respectively.

An output 276 of error signal generator 240 is coupled to an input 278of PI controller 250. An output of 280 of PI controller 250 is coupledthrough PWM enables 256, 258 to data inputs 281, 282 of PWM signalgenerators 256, 258, respectively. An output 283 of PWM signal generator256 is coupled to a control input 284 of power signal driver 260. Anoutput 285 of PWM signal generator 258 is coupled to a control input 286of power signal driver 262.

ECU 244 includes a power terminal 287 coupled through contacts 132 ofautomatic shutdown relay 134 of power distribution center 108 andthrough fuse 136 of power distribution center 108 to positive terminals218, 234 of batteries A and B. Power inputs 296, 298 of power signaldrivers 260, 262, respectively, are coupled to power terminal 287. Oneside of field windings 292 of alternator A is coupled to power output294 of power signal driver 260 at output terminal 294 of ECU 244 (whichis also coupled to power output 294 of power signal driver 260). Theother side of field windings 292 is coupled to ground. One side of fieldwinding 295 of alternator B is coupled to power output 296 of powersignal driver 262 at output terminal 297 of ECU 244 (which is alsocoupled to power output 296 of power signal driver 262). The other sideof field windings 295 is coupled to ground.

In an aspect, electronic voltage regulator 246 has the same basicelements as electronic voltage regulator 112. While electronic voltageregulator 246 is illustratively implemented in ECU 244, it should beunderstood that it could be implemented as a separate, stand-alonedevice.

Positive terminal 218 of battery A is coupled to positive terminal 234of battery B by crossover line 299, which keeps the outputs ofalternators A and B at a common level. It should be understood that ifelectrical system 200 has more than two alternators, the outputs of allthe alternators are tied together to keep their outputs at a commonlevel.

In electrical systems having multiple alternators, when the output ofone of these alternators fails it is usually not readily apparent to thedriver that the charging capability has been significantly reduced.Different strategies have been employed in the past to detect the lostoutput, all of which involve measuring the output voltage of thealternators under various operating scenarios.

In accordance with an aspect of the present disclosure, detection of thefailure of an output of an alternator in an electrical system, such aselectrical system 200, having multiple alternators is based on theresponse of the charging control system when the PWM drive signal to thefield windings of one of the alternators is disabled (for example, setto have a zero percent duty cycle) and whether this response results inan increase in the duty cycle of the PWM drive signal. Illustratively,the duty cycle calculated by the PI controller 250 for the PWM drivesignal is used in this. When all the alternators in the electricalsystem are functioning properly, temporarily disabling the PWM drivesignal to the field windings of one of the alternators results in anincrease in the duty cycle for the PWM drive signal calculated by PIcontroller 250. The PI controller 250 recognizes the reduction incurrent available from the alternators and compensates by increasing theduty cycle it calculates for the PWM drive signal. Failure of analternator is detected when temporarily disabling the PWM drive signalto the field winding of that alternator does not result in an increasein the duty cycle calculated by the PI controller 250 for the PWM drivesignal to the field windings of one or more of the other alternators.

With reference to the example electrical system 200 shown in FIG. 2,electronic voltage regulator 246 maintains a constant system voltage bycontrolling the duty cycle of the PWM drive signals applied to the fieldwindings 292, 295 of the respective alternator A, B. When the field foran alternator A, B is off, the electrical current in electrical system200 is maintained by the batteries A, B. As the system voltage begins todecrease, the field windings 292, 295 of alternators A, B are energizedand the alternators A, B replace the lost charge of the batteries A, Band the system voltage is increased. Each voltage sense output 224, 240provides an accurate measurement of the system voltage as it relates toeach battery A, B. As the load on electrical system 200 changes, thetarget voltage (which is the desired system voltage) is adjusted basedon the actual system voltage as measured by the ECU 244 and an errorterm is calculated based on the sense voltages at voltage sense inputs264, 266 of ECU 244 and a target voltage determined by voltage targetgenerator 268 of ECU 244. Illustratively, the voltage sense output 224of alternator A is used by ECU 244 in calculating this error term unlessalternator A has failed. If alternator A has failed, ECU 244 uses thevoltage sense output 240 of alternator B to determine this error term.PI controller 250 then uses this error term to adjust the duty cycle itcalculates for the PWM drive signal that is applied to the respectivefield windings 292, 295 of alternators A, B. Each alternator A, B thenacts in tandem to increase the power available for the entire electricalsystem 200.

If the PWM drive signal to the respective field windings 292, 295 ofeach alternator A, B is intentionally interrupted asynchronously, thendue to the reduced system capacity the error term between the targetvoltage and the sense voltage will increase resulting in PI controller250 calculating a higher duty cycle for the PWM drive signal. Thedetection of this change confirms the contribution of the alternator Aor B that has had the PWM drive signal to it its field windingsinterrupted and may be used as an input to diagnose a faulty alternator.The process may then be applied to the other alternator A, B in likefashion and thereby confirm the proper charging operation. In should beunderstood that if there are more than two alternators, this process canbe applied equally to each of the alternators. In this regard, ECU 244selects in turn the alternators to be evaluated and evaluates one of thealternators during each evaluation cycle. ECU 244 illustrativelycontrols PWM enable 252 and PWM enable 254 to disable the PWM drivesignal being applied to a respective field winding 292, 295.

FIGS. 3A and 3B are a flow chart showing of illustrative program logicprogrammed into a controller for an evaluation routine that implementsthe foregoing method. This controller is illustratively ECU 244, but itshould be understood that this controller could be another device, suchas a stand-alone controller coupled to electronic voltage regulator 246,such as if electronic voltage regulator 246 was a separate device fromthe engine control module of vehicle 202.

The discussion of the following evaluation routine shown in the flowchart of FIGS. 3A and 3B focuses on an application with two alternatorsand is discussed with reference to electrical system 200 havingalternators A, B. This evaluation routine may be simply expanded toevaluate any number of alternators.

ECU 244 starts the evaluation routine at 300 in FIG. 3A and at 302,determines if enabling conditions are met to proceed with evaluating thealternators A, B. The presence of certain conditions may prevent anaccurate evaluation of the alternators and if any of these conditionsare present, then the enabling conditions are not met. One suchcondition, by way of example, is when the calculated duty cycle for PWMdrive signal is near its maximum. If the enabling conditions are notsatisfied, ECU 244 exits the evaluation routine at 304. If the enablingconditions are satisfied, ECU 244 proceeds to 306 where it determineswhich of the alternators is to be evaluated. Illustratively, thealternators are evaluated sequentially, with one alternator beingevaluated during each evaluation cycle. If at 306 ECU 244 determinesthat alternator A was evaluated during the last evaluation cycle, itselects alternator B for evaluation for this evaluation cycle andbranches to 308. At 308, ECU 244 checks if alternator B had failedpreviously. If alternator B had failed previously (that is, analternator B test fail flag has been set), ECU 244 exits the evaluationroutine at 310. If alternator B had not failed in the last evaluation,at 312 ECU 244 disables the PWM drive signal to the field windings 295of alternator B and proceeds to 314 where it checks if the duty cycle ofthe PWM drive signal calculated by PI controller 250 has increased by apredetermined amount. This predetermined amount is an amount that issufficient to indicate that disabling alternator B has caused anappreciable drop in system output voltage and the electronic voltageregulator 246 is compensating for that drop by increasing the output ofalternator A by increasing the duty cycle of the PWM drive signalapplied to the field windings 292 of alternator A. It should beunderstood that this predetermined amount may be a calibratable amountand settable by setting the value for the appropriate calibrationparameter in a calibration set programmed into ECU 244. It should beunderstood that this predetermined amount can be determinedheuristically.

If the duty cycle calculated by PI controller 250 for the PWM drivesignal has increased by the predetermined amount, there is a highprobability that alternator B is working properly and ECU 244 thenproceeds to 316 where ECU 244 sets an alternator B test pass flag andthen proceeds to 318, where ECU 244 clears the alternator B test failflag. ECU 244 then proceeds to 320 where it sets a flag that alternatorB was tested during the present evaluation cycle and then at 322, clearsa flag that alternator A was tested during the present evaluation cycle.ECU 244 then branches to 324 where it causes the PWM drive signal tofield windings 295 of alternator B to be enabled, and at 326, exits theevaluation routine.

Returning to 314, if ECU 244 determines that the duty cycle calculatedby PI controller 250 for the PWM drive signal did not increase thepredetermined amount, it branches to 328 where it checks whethersufficient time has passed to allow electronic voltage regulator 246 torespond to a decrease in system voltage and increase the duty cycle ofthe PWM drive signal. If not, ECU 244 branches back to 314. Ifsufficient time has passed, there is a high probability that alternatorB has failed and ECU branches to 330 where it sets the alternator B testfail flag and then at 332, clears the alternator B test pass flag. ECUthen branches to 320. In this regard, the PWM drive signal to the fieldwindings 295 of alternator B is re-enabled regardless of pass/failstatus so that an intermittent failure does not completely shut downsome contributions from alternator B.

It should be understood that in electrical system having more than twoalternators, the duty cycle of the PWM drive signal applied to the fieldwindings of any one (or all) of the alternators not being evaluated inthe present evaluation cycle can be checked to determine if thealternator being evaluated in the present evaluation cycle has beenfailed.

The above described steps are mirrored for each of the other alternatorsin the electrical system. Again referring to electrical system 200 as anexample and returning to 306, if ECU 244 selects alternator A forevaluation it mirrors the above steps which are identified with acorresponding reference with a “prime.” For example, reference number308′ instead of 308. In this regard, it should be understood that thereis an alternator test pass and an alternator test fail flag for eachalternator in the electrical system. The PWM drive signal applied to thefield windings of the alternator being evaluated is disabled to evaluatethat alternator and the duty cycle calculated by PI controller 250 forthe PWM drive signal is checked to determine if the alternator beingevaluated has failed.

In accordance with another aspect of the present disclosure, ECU 244causes the PWM drive signals applied to the field windings of therespective alternators to be out of phase with each other. Morespecifically, the phase relationship among the PWM drive signals isdetermined by 360/X where X is the number of alternators in theelectrical system. For example, with reference to FIG. 4, in electricalsystem 200 which has two alternators, the PWM drive signals 400, 402applied to the field windings 292, 295 of alternators A and B,respectively, are one-hundred and eighty degrees out of phase with eachother, as shown in FIG. 4.

While the preferred embodiment utilizes a single electronic voltageregulator (electronic voltage regulator 246) implemented in ECU 244, itshould be understood that multiple electronic voltage regulators, onefor each electrical generating machine, can also be utilized. FIG. 5shows an embodiment in which two electronic voltage regulators 112(FIG. 1) are implemented in an ECU 244′ with each electronic voltageregulator 112 generating the PWM drive signal for a respective one ofthe respective field windings 292, 294 (FIG. 2) of the respectivealternator A, B.

What is claimed is:
 1. An electrical system for an automotive vehicle, comprising: a plurality of electrical generating machines with each electrical generating each electrical generating machine including field windings energized by pulse width modulated drive signals generated by an external electronic voltage regulator, the pulse width modulated drive signals having a duty cycle determined by the electronic voltage regulator, the electronic voltage regulator varying the duty cycle of the pulse width modulated drive signals to control output voltages of the electrical generating machines; a controller, the controller selecting one of electrical generating machines to evaluate for failure and evaluating that electrical generating machine for failure by causing the PWM drive signal for the field windings of that electrical generating machine to be disabled and then determining that this electrical generating machine has failed if the duty cycle for the PWM drive signals has then not been increased by the electronic voltage regulator by a pre-determined amount after the PWM drive signal for the field windings of that electrical generating machine has been disabled.
 2. The electrical system of claim 1 wherein the controller evaluates in turn each of the electrical generating machines.
 3. The electrical system of claim 1 wherein the electrical generating machines are alternators or generators.
 4. The electrical system of claim 1 wherein the controller includes the electronic voltage regulator and causes the PWM drive signals generated by the electronic voltage regulators to be out of phase with each other.
 5. The electrical system of claim 4 wherein the controller is an engine control module.
 6. The electrical system of claim 5 wherein the electronic voltage regulator includes a PWM driver for each electrical generating machine, each PWM driver coupled to the field windings of a respective one of the electrical generating machines.
 7. The electrical system of claim 4 wherein the controller causes the PWM drive signals to be out of phase with each other a number of degrees determined by 360/X where X is the number of electrical generating machines that the electrical system has.
 8. The electrical system of claim 1 wherein the electronic voltage regulator includes an electronic voltage regulator for each electrical generating machine.
 9. In an electrical system for an automotive vehicle having a plurality of electrical generating machines with each electrical generating including field windings energized by a pulse width modulated drive signals generated by an external electronic voltage regulator, the pulse width modulated drive signals having a duty cycle determined by the electronic voltage regulator, the electronic voltage regulator varying the duty cycle of the pulse width modulated drive signals to control output voltages of the electrical generating machines, a method of evaluating whether any of the electrical generating machines has failed, comprising: selecting one of electrical generating machines to evaluate for failure and evaluating that electrical generating machine for failure by disabling the PWM drive signal being provided to the field windings of that electrical generating machine; and then determining that this electrical generating machine has failed if the duty cycle of the PWM drive signals has then not been increased by the electronic voltage regulator by a predetermined amount after the PWM drive signal for the field windings of that electrical generating machine has been disabled.
 10. The method of claim 9 wherein each of the electrical generating machines are evaluated for failure in turn.
 11. The method of claim 10 including generating the PWM drive signals so that the PWM drive signals are out of phase with each other.
 12. The method of claim 11 wherein the PWM drive signals are out of phase with each other a number of degrees determined by 360/X where X is the number of electrical generating machines that the electrical system has.
 13. An electrical system for an automotive vehicle, comprising: a plurality of electrical generating machines with each electrical generating each electrical generating machine including field windings energized by pulse width modulated drive signals generated by an external electronic voltage regulator, the pulse width modulated drive signals having a duty cycle determined by the electronic voltage regulator, the electronic voltage regulator varying the duty cycle of the pulse width modulated drive signals to control output voltages of the electrical generating machines; and a controller that includes the electronic voltage regulator, the controller causing the PWM drive signals to be out of phase with each other.
 14. The electrical system of claim 13 wherein the controller causes the PWM drive signals to be out of phase with each other a number of degrees determined by 360/X where X is the number of electrical generating machines that the electrical system has.
 15. The electrical system of claim 13 wherein the electrical generating machines are alternators or generators.
 16. The electrical system of claim 13 wherein the controller is an engine control module.
 17. The electrical system of claim 13 wherein the electronic voltage regulator includes an electronic voltage regulator for each electrical generating machine. 